Questions to Ponder When You Should Be Working

Why is it that when a cat takes a crap in a litter box, inside a house, it is considered "litter trained", yet when a dog defecates on the floor inside of a home, one does not call it "house trained"? Generally, a dog is considered to be "house trained" when it is noted that the canine is able to hold it's feces in until it is let outside to shit in the yard. The more accurate term would be "yard trained." No? Maybe?